1. Technical Field
The invention relates to air bearing sliders, and, more particularly, to low stiction air bearing sliders.
2. Description of the Prior Art
Magnetic storage devices typically include a magnetic storage disk having a plurality of tracks for storing data, and a slider to which is secured a transducer for reading data from and writing data to each of the tracks. For most high capacity magnetic storage applications, when the disk is at rest, the slider contacts the disk. When the disk rotates, the slider provides an air bearing between the rotating disk and the transducer. In order to function properly, the slider must maintain the following: proper fly height and adequate roll, pitch and normal stiffness over the predetermined data band, corresponding to a range of operating speeds, and over the predetermined range of skew angles (i.e. angle between the longitudinal axis of the slider and the tangential disk velocity vector); low takeoff speed; low stiction at start-up; and insensitivity to wear and debris. Proper fly height and adequate air bearing stiffness are provided so that the slider does not contact the disk, thus avoiding disk damage and data read/write errors. Similarly, low takeoff speed and low stiction at start-up limit disk damage during takeoff and landing as well as slider wear.
Moreover, as magnetic storage systems are designed for higher and higher recording densities, the air bearing gap between the transducer and the rotating disk is reduced. A requirement for achieving a small air bearing gap is increased smoothness of the disk. As a rule, this leads to increased stiction. In the most commonly used air bearing designs, namely railed, taper-flat sliders, the slider and the disk have substantial apparent contact area upon standstill, giving rise to increased stiction.
To avoid stiction, an approach commonly known as load/unload has been commercialized. During the load operation, the slider is deftly lowered onto a rotating disk. During the unload operation, the slider is lifted off the disk prior to stopping the disk. Because contact between the slider and the disk is avoided altogether, the effects of stiction are averted. Details of the load/unload operation may be found in R. M. Crone, M. S. Jhon, B. Bhushan, T. Karis, Numerical Simulation of Dynamic Slider Loading and Transient Slider Response to Surface Defects, Adv. Info. Storage Syst., Vol. 3, 1991, pp. 15-31, and U.S. Pat. No. 5,189,575. However, this approach is relatively costly and may lead to contamination of the read/write head assembly, which occurs when the arm that carries the read/write head assembly slides in contact with a surface which is tilted relative to the disk and generates microscopic wear particles. Consequently, starting and stopping the slider in contact with the disk is still a widespread approach.
To limit stiction when the slider is started and stopped in contact with the disk, the prior art evidences a number of techniques. For example, commonly assigned U.S. Pat. No. 4,420,780 to Deckert discloses a slider having rails with lengthwise curvature (known in the industry as crowned rails) for limiting stiction. However, it is apparent that the slider can rock on the disk surface giving rise to delayed takeoff and early landing. Moreover, even though the apparent contact area of such a slider is nearly zero, the actual contact area is uncertain due to elastic deformation of the disk asperities and possible wicking of liquid (such as water vapor) into the disk/slider gap.
Furthermore, it is common practice to apply a lubricant on the disk. The lubricant may be a mobile liquid or a liquid chemically bound to the surface of the disk. However, while beneficial from the point of view of disk durability and protection of the disk surface against inadvertent contact, lubricants aggravate the stiction problem (i.e., too little affords too little protection against wear; too much leads to unacceptable stiction). For this reason, the amount of lubricant must be carefully metered in harmony with the disk roughness.
Accordingly, there remains a need in the art for a slider that provides proper fly height, adequate air bearing stiffness and also low stiction such that the slider is suitable for use in high density recording systems having a minimal air bearing gap. In particular, there is a need for a slider design with minimal actual contact area. Although there are slider designs that have zero apparent contact area, such as the cited patent to Deckert, the actual contact area is uncertain due to the causes described above (wicking, etc.).